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196                                      FLORA   INDICA.
obliquely to the axis of the chain that they have a long course
through a moderately dry climate. The valleys of the other
rivers (except the Jelam) are much more perpendicular to
the axis, and the humid vegetation passes almost immediately
into an alpine and Tibetan flora, without the intervention of
a dry temperate flora.
It must not be supposed that the'vegetation of the interior
temperate Himalaya is altogether, or even in a great measure,
different from that of the outer ranges. A very large propor-
tion of the species is the same throughout both regions, con-
sisting of western forms, to which even heavy rain at one sea-
son is not injurious so long as a great portion of the year is
dry, but whose progress to the east is- stopped as soon as the
humidity becomes permanent. The rains' vegetation of the
outer mountains is, however, entirely absent from the inte-
rior, and its place is taken by such Tibetan forms as are not
entirely intolerant of moisture. The presence of Pinus GV
rardiana, Ephedra, 'Quercus Ilex, Ribes Grossularia, and Dian-
thus, may be considered as indicating that the rains are very
- trifling in amount in average seasons. Pinus lonf/ifolia disap-
pears, with Rhododendron arbor eum and its associated plants;
but all the other pines continue to the upper limit of trees, or
to the borders of Tibet. The cultivation of the vine is only
carried on in this inner region, the rainy season of the outer
mountains preventing the ripening of grapes.
West of the Ravi the rain-fall has so much lessened even on
the outer hills, that it is only on the first range which rises
into the temperate zone, that the normal West Himalayan
vegetation (Quercus incana, etc.) occurs; while the valleys im-
mediately north of it, when Sheltered by "hills rising conti-
nuously to*9000 or 10,000 feet, present many of the features
characteristic of the interior Himalaya. The presence or ab-
sence of Quercus incana, Rhododendron arboreuw, and Andro-
meda ovtdifolia, on the one hand, and of Pbius Gerardlana
and EpJtedra on the other, may be regarded ať a fair criterion
of the two extreme climates; but there are many valleys in